TU-EF-304-11: Therapeutic Benefits of Collimation in Spot Scanning Proton Therapy in the Treatment of Brain Cancer

Journal Article · Mon Jun 15 04:00:00 EDT 2015 · Medical Physics

DOI:https://doi.org/10.1118/1.4925666· OSTI ID:22565371

Moignier, A; Gelover, E; Wang, D; Flynn, R; Hyer, D ^[1]; Kirk, M; Lin, L; Solberg, T; Lin, A ^[2]

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1. Department of Radiation Oncology, University of Iowa, Iowa City, IA (United States)
2. Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA (United States)

Purpose: A dynamic collimation system (DCS) based on two orthogonal pairs of mobile trimmer blades has recently been proposed to reduce the lateral penumbra in spot scanning proton therapy (SSPT). The purpose of this work is to quantify the therapeutic benefit of using the DCS for SSPT of brain cancer by comparing un-collimated and collimated treatment plans. Methods: Un-collimated and collimated brain treatment plans were created for five patients, previously treated with SSPT, using an in-house treatment planning system capable of modeling collimated and un-collimated beamlets. Un-collimated plans reproduced the clinically delivered plans in terms of target coverage and organ-at-risk (OAR) sparing, whereas collimated plans were re-optimized to improve the organ-at-risk sparing while maintaining target coverage. Physical and biological comparison metrics such as dose distribution conformity, mean and maximum doses, normal tissue complication probability (NTCP) and risk of secondary brain cancer were used to evaluate the plans. Results: The DCS systematically improved the dose distribution conformity while preserving the target coverage. The average reduction of the mean dose to the 10-mm ring surrounding the target and the healthy brain were 7.1% (95% CI: 4.2%–9.9%; p<0.01) and 14.3% (95% CI: 7.8%–20.8%; p<0.01), respectively. This yielded an average reduction of 12.0% (95% CI: 8.2%–15.7%; p<0.01) for the brain necrosis NTCP using the Flickinger model, and 14.2% (95% CI: 7.7%–20.8%; p<0.01) for the risk of secondary brain cancer. The average maximum dose reductions for the brainstem, chiasm, optic nerves, cochleae and pituitary gland when comparing un-collimated and collimated plans were 14.3%, 10.4%, 11.2%, 13.0%, 12.9% and 3.4%, respectively. Evaluating individual plans using the Lyman-Kutcher-Burman NTCP model also yielded improvements. Conclusion: The lateral penumbra reduction performed by the DCS increases the normal tissue sparing capabilities of SSPT for brain tumor treatment while preserving the target coverage. This research was financially supported by Ion Beam Applications S.A. (IBA, Louvain-La-Neuve, Belgium)

• OSTI ID: 22565371
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 6 Vol. 42; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

60 APPLIED LIFE SCIENCES
61 RADIATION PROTECTION AND DOSIMETRY
ANIMAL TISSUES
BRAIN
HAZARDS
ION BEAMS
NECROSIS
NEOPLASMS
NERVES
PATIENTS
PITUITARY GLAND
PROTON BEAMS
RADIATION DOSE DISTRIBUTIONS
RADIATION DOSES
RADIOTHERAPY